In many operating environments, it is often necessary to transmit mechanical force and motion from outside a sealed area to inside the sealed area. For example, semi-conductor manufacturing requires environmentally sealed and clean areas for fabrication of semiconductor waffers, often in a vacuum. The fabrication often requires the rotation of a wafer in a vacuum chamber.
Feedthrough devices have been developed to transmit mechanical force and motion from outside of the sealed area to inside of the sealed area. The feedthroughs allow manipulation of objects and materials inside the sealed chambers while maintaining minimal, and preferably zero, leakage. This eliminates the need to open the chamber to apply motion to devices inside.
Rotary type feedthrough devices provide shaft rotation inside the chamber area while maintaining the integrity of the seal. Single axle rotary feedthrough devices are disclosed in, for example, U.S. Pat. Nos. 1,441,794; 3,782,685; 4,646,579; 4,136,444; 2,497,867; 5,243,867; 3,051,008; 4,885,947; 6,119,537; and 2010/0105487, the disclosures of which are incorporated herein by reference as if set out in full. In some applications, the rotational motion needs to be applied to objects in one or more of the following: a co-rotational direction but at different speeds, a counter rotational direction at the same of different speeds, combinations therein, or the like. To accomplish multiple rotational movements, dual coaxial, hermetically sealed, rotary shaft feedthrough devices have been developed. Dual rotary feedthrough devices are disclosed in, for example, U.S. Pat. Nos. 4,885,947 and 4,683,763, the disclosure of which is incorporated herein by reference as if set out in full.
Generally, conventional dual coaxial rotational feedthrough devices are a higher level manifestation of basic single axis rotary shaft feedthrough devices associated with the above incorporated prior art, which have a long and successful history. More complex modern equipment demands greater degrees of freedom through and into the chambers and all combined in a smaller package. Wide demand is seen in vacuum and semiconductor processing equipment where materials are introduced and processed in complex ways inside sealed chambers requiring movements inside the sealed chamber.
All existing prior art involves using at least two metallic bellows as the outer member. Another single axis feedthrough device is added in series and attached to the metallic bellows in order to add a second shaft. This arrangement has several drawbacks. One drawback includes the fact that the design is long in length, which can cause undesirable moment arms. The length is due in part to combining at least two units together in series. Common length-to-diameter ratios are about 5:1 for this configuration. A second drawback of the existing arrangements includes the complexity and precision required to fabricate devices that work acceptably. Still another drawback includes a cumbersome internal configuration that limits conventional designs in both rotational speed and torque that can be transmitted. Other drawbacks, problems, and deficiencies may exist for current dual coaxial rotary feedthrough devices.
In view of the above, improved coaxial rotary feedthrough devices are desirable.